In a known technology, in order to minimize a shift shock to the body of a vehicle which may be caused by a friction element (e.g., clutch or brake) in an automatic transmission of the vehicle being rapidly applied by the initial hydraulic pressure supplied thereto, an automatic transmission damper mechanism is used which includes an accumulator and an orifice both provided in a hydraulic passage dedicated to damping the hydraulic pressure (e.g., Refer to Japanese Patent Application Publication No. 11-153214 (JP-A-11-153214)). Further, FIG. 6 shows another known automatic transmission damper mechanism that has: a damper 30 constituted of a slide member 31, an elastic member 32, a container containing these members; a first hydraulic pipe 42 one end of which is connected to a pump 41 and the other end of which is connected to the damper 30; a second hydraulic pipe 43 one end of which is connected to the damper 30 and the other end of which is connected to a friction element 46, an orifice 44 provided between the first hydraulic pipe 42 and the second hydraulic pipe 43; a branch pipe 45 branching from the first hydraulic pipe 42 and extending to the second hydraulic pipe 43, and a check valve 47 provided midway in the branch pipe 43 so that the damper 30 and the check valve 47 are located in parallel.
According to the former related-art automatic transmission damper mechanisms, however, because the accumulator and the orifice are provided in the hydraulic passage as pressure damping elements, the following problems are concerned. That is, because the diameter of the orifice is not variable and it is provided in the hydraulic passage separately from the accumulator, the rising of the hydraulic pressure from the level at the beginning of the hydraulic pressure supply to the level required to apply the friction element is gentle, which may cause an operation response delay. Further, according to the above-described automatic transmission damper mechanisms, the damping function for absorbing hydraulic pressure overshooting is in effect until the hydraulic pressure supplied to the friction element reaches the level required to apply the friction element, and when the hydraulic pressure reaches the application level, the damping friction is cancelled. This feature requires another circuit means and another controller, which makes the system configuration further complicated. Likewise, in the related-art damper mechanism shown in FIG. 6, the fixed-diameter orifice 44 and the damper 30 are separately located in parallel. Therefore, the rising of the hydraulic pressure from the level at the beginning of the hydraulic pressure supply to the level required to apply the friction element is gentle, which may cause an operation delay.